Pulse transmission transceiver architecture for low power communications

ABSTRACT

Systems and methods for pulse-transmission low-power communication modes are disclosed. A method of pulse transmission communications includes: generating a modulated pulse signal waveform; transforming said modulated pulse signal waveform into at least one higher-order derivative waveform; and transmitting said at least one higher-order derivative waveform as an emitted pulse. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSOREDRESEARCH AND DEVELOPMENT

[0001] This invention was made with Government support under contractNo. DE-AC05-96OR22464 awarded by the United States Department of Energyto Lockheed Martin Energy Research Corporation, and the Government hascertain rights in this invention.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates generally to the field of pulsetransmission communications. More particularly, the invention relates topulse transmission, spread-spectrum modes of low-power radiocommunications.

[0004] 2. Discussion of the Related Art

[0005] Prior art time-domain communications techniques are known tothose skilled in the art. The bandwidth and center frequency of aconventional time-domain transmission are both explicit functions of thepulse width.

[0006] In these techniques, the controllable parameters are the pulsewidth and power. These techniques normally allow only 1 bit to beconveyed per transmitted pulse, thereby limiting their communicationsusefulness.

[0007] A problem with this existing technology has been that theparameters of pulse width and power effectively provide only two degreesof freedom. This constraint severely limits the flexibility of theprior-art time-domain techniques. Therefore, what is required is anapproach to time-domain communications that provides more degrees offreedom.

[0008] Another problem with this existing technology has been that onlyone bit can be encoded per transmitted pulse. This constraint severelylimits the data bandwidth of the prior art time-domain techniques.Therefore, what is also required is an approach to time-domaincommunications that permits more than one bit per pulse to becommunicated.

[0009] Heretofore, the requirements of providing additional degrees offreedom and communicating multiple bits per pulse have not been fullymet. What is needed is an approach that can address both of theserequirements. The invention is directed to meeting these requirements,among others.

SUMMARY OF THE INVENTION

[0010] The main object of the invention is to provide a versatile,multi-bit, very broadband, high bit-rate data communications method.Another goal of the invention is to use higher-order derivatives ofpulsed (time-domain) signals to satisfy the above-discussed requirementsof providing additional degrees of freedom and communicating multiplebits per pulse which, in the case of the prior art, are notsimultaneously satisfied.

[0011] One embodiment of the invention is based on a method ofpulse-transmission communications, comprising: generating a modulatedpulse-signal waveform; transforming said modulated pulse-signal waveforminto at least one higher-order derivative waveform; and transmittingsaid at least one higher-order derivative waveform as an emitted pulse.Information is preferentially encoded as the derivative order and phase;alternatively, time derivatives between pulses can also encodeinformation. In the latter case, the higher-order derivative pulseprovides flexible control over bandwidth and band center-frequency, thusalleviating noise and other interference problems. Another embodiment ofthe invention is based on an electromagnetic waveform, comprising: anemitted pulse that is produced from at least one higher-order derivativewaveform of a modulated pulse-signal waveform. Another embodiment of theinvention is based on an apparatus based on an array of varioushigher-order derivative-pulse generators, each of which is modulated byan information signal. The modulated derivative pulses are summed,amplified, and coupled to a transmission medium (antenna, cable, opticalfiber, etc.) The complementary receiver recovers the modulated pulsesvia standard correlation.

[0012] These, and other, goals and embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingpreferred embodiments of the invention and numerous specific detailsthereof, is given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of the inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A clear conception of the advantages and features constitutingthe invention, and of the components and operation of model systemsprovided with the invention, will become more readily apparent byreferring to the exemplary, and therefore nonlimiting, embodimentsillustrated in the drawings accompanying and forming a part of thisspecification, wherein like reference characters designate the sameparts. It should be noted that the features illustrated in the drawingsare not necessarily drawn to scale.

[0014]FIG. 1 illustrates a series of Gaussian derivative wavelets infrequency space, representing an embodiment of the invention.

[0015]FIG. 2 illustrates a high-level schematic diagram of a circuit forgenerating a second-derivative Gaussian wavelet, representing anembodiment of the invention.

[0016]FIG. 3 illustrates center frequency as a function of derivativeorder, representing an embodiment of the invention.

[0017]FIG. 4 illustrates relative bandwidth as a function of derivativeorder, representing an embodiment of the invention.

[0018]FIG. 5 illustrates the power spectrum of a 7th-order Gaussianpulse, representing an embodiment of the invention.

[0019]FIG. 6 illustrates a series of Gaussian derivative time-domainpulses, representing an embodiment of the invention.

[0020]FIG. 7 illustrates a series of 7 superimposed Gaussian derivativepulses of orders 2-8 composing a set of symbol codes, representing anembodiment of the invention.

[0021]FIG. 8 illustrates a composite pulse representing the binary code0 1 01 11 01, representing an embodiment of the invention.

[0022]FIG. 9 illustrates the power spectral density of the compositepulse depicted in FIG. 8.

[0023]FIG. 10 illustrates a high-level schematic diagram of a circuitfor transmitting, representing an embodiment of the invention.

[0024]FIG. 11 illustrates a high-level schematic diagram of a circuitfor receiving, representing an embodiment of the invention.

[0025]FIG. 12 illustrates a high-level schematic of a circuit fortransmitting, representing an embodiment of the invention.

[0026]FIG. 13 illustrates a high-level schematic of another circuit fortransmitting, representing an embodiment of the invention.

[0027]FIG. 14 illustrates a high-level schematic of another circuit forreceiving, representing an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] The invention and the various features and advantageous detailsthereof are explained more fully with reference to the nonlimitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description of preferred embodiments.Descriptions of well known components and processing techniques areomitted so as not to unnecessarily obscure the invention in detail.

[0029] The context of the invention is spread-spectrum communications.For instance, the invention can be used in the context of low-powerspread-spectrum radio communications. The invention can also utilizedata processing methods that transform the received pulse transmissionsignals so as to actuate interconnected discrete hardware elements; forexample, to remotely reconfigure repeater(s) and/or router(s).

[0030] The invention includes using higher-order derivatives ofwaveforms to implement pulse transmission communications, whereby theshape as well as the bandwidth and center frequency of the transmittedpower pulse may be used as adjustable parameters allowing a moreversatile transmission architecture. In addition, the higher-derivativepulses may be used as the basis of a multiple-bit symbol system, greatlyincreasing the transmitted information rate.

[0031] The phrase “higher-order derivative,” as used herein, is definedas at least a second order derivative (i.e., 2nd order, 3rd order, . . .nth order). The term “approximately”, as used herein, is defined as atleast close to a given value (e.g., preferably within 10% of, morepreferably within 1% of, and most preferably within 0.1% of). The term“coupled”, as used herein, is defined as connected, although notnecessarily directly, and not necessarily mechanically. The term“programmable”, as used herein, is as defined controllable by two ormore lines of code that can be executed by a computer.

[0032] The term “orthogonal,” as used herein, is defined as two or morefunctions or signals whose overlap is zero. The practical advantage ofusing orthogonal signals is that they do not interfere with each otherand they are independent, which means that information carried by onecan be inserted or extracted independently of the information in theother. For instance, a sine and a cosine signal each of the samefrequency are orthogonal; quadrature signals are orthogonal.

[0033] The invention provides another degree of freedom (shape) tocontrol the transmission's spectral properties, thereby allowing a widerrange of applications, greater receiver selectivity, and the ability toavoid known interferers and reduce potentially harmful interference toexisting radio frequency (RF) services and users. The invention allowsreduced emissions in lower-frequency regions compared to those of theprior art. This will reduce interference to existing radio frequencyservices and users. The invention can (for a given spectral content)permit longer generating pulse widths and easier electronicimplementation, ensuring compatibility with existing commercial devicesand processes.

[0034] The invention can include the capability of implementing thesecontrollable parameters directly in radio-frequency (RF) silicon bipolaror complementary metal-oxide semiconductor (CMOS) devices, as well aswith silicon-germanium (SiGe), gallium arsenide (GaAs), or othersuitable high-frequency semiconductor processes. Use of these processescan make implementations of the invention inexpensive to fabricate andfast enough to be operable at VHF/UHF frequencies (hundreds of MHz) andbeyond.

[0035] The invention can include generating waveforms from storeddigital versions. This can simplify the hardware requirements fortransmitters.

[0036] The invention can be combined with orthogonal time hopping,orthogonal frequency hopping, and hybrid frequency/time methods. Bytransmitting a data stream at various intervals and/or at variousfrequency bands, the pulse transmission can be made difficult to detect,much less decode.

Mathematical Background

[0037] By passing a rectangular pulse of chosen duration through ashaping circuit, a Gaussian waveform (or other type of waveform usefulfor communications) may be produced. Electronic circuitry for achievingsuch pulse shaping is widely described in the nuclear-detectionliterature. The resulting Gaussian pulse is then amplified as requiredand passed through further circuitry that effects a predetermined numberof derivatives; the output pulse is a waveform closely approximating thedesired-order derivative of an ideal Gaussian function. The pulse ofdesired derivative order is then linearly amplified and matched to theantenna of choice for transmission. Alternatively, lattice-filterstructures can directly achieve the desired derivative order, startingwith a simple bipolar input pulse.

[0038] Although the Gaussian-derivative pulse family is the preferredembodiment for practicing the invention, such practice is not limited toGaussian pulses. In general, any family of pulses which derives from asingle or multiple pulses that have a limited extent in both time andfrequency are suitable for shaping and modulating as carriers ofinformation as described herein. The derivative-derived familynecessarily obeys a Rodriques' Formula; other band-limited andtime-limited orthogonal functions do not, yet can serve as a family ofpulses suitable to the purposes of the invention. The convenience of theGaussian pulse stems from its unique property that both function and itsFourier transform have the same functional form, namely exp (−x^(2n)/a)where a is a constant and x is either time or frequency. Some functionsthat are similarly bounded in time and frequency are the“super-gaussian” functions described by exp (−x^(2n)/a) where n is aninteger>1 that represents the order of the function.

[0039] In addition, it is not required that the fundamental member(s) ofthe pulse family possess a convenient functional form. A time-limitedsquare pulse can be shaped to restrict its frequency content by“rounding” the “corners,” giving a smooth “square” pulse. Such a pulsemeets the requiremens of limited support in both time and frequency.Derivatives of such a pulse, while not necessarily orthogonal, can carryinformation and be demodulated as described herein.

[0040] Another class of functions that can serve as the orthogonalfamily for the practice of the invention is the so-called discretefunctions. Members include the Chebyshev and Krawtchouk polynomials,which are defined on a finite lattice (sample points) rather than acontinuous segment. These families are suitable candidates forpracticing the invention using pulses reconstituted from stored samplesas previously suggested.

[0041] In general mathematical terms, any “lump” sufficientlyconcentrated in both time and frequency can possess either a derivativefamily or a family stored as discrete samples meeting the practicalorthogonality and practical spectral requirements on which the practiceof the invention is based. The choice of the particular shape of theroot or basic member of the family is purely a practical matter, havingto do with the particular means of electrically generating the pulsesand coupling them to a properly designed antenna. Issues of signalpropagation and reception can also play a design role in specific andindividual situations.

[0042]FIG. 1 shows Gaussian-derivative wavelets in frequency space. Thederivative orders from 1 to 13 are shown as a function of frequency. Asthe derivative order is increased, the mode of the function (centerfrequency) moves from near zero (or dc frequency) to higher values asshown in FIG. 1. The first-derivative pulse, shown as the dashed curve,used in communication systems according to the prior art, has a slope ofτ{square root}{square root over ( )}π at zero frequency, indicatingconsiderable spectral power at low frequencies; the higher derivativesall have zero slope at zero frequency, indicating very little energy atlow frequencies. If the initial square pulse is 1 ns wide, the abscissais in GHz. The ordinate is in normalized power units.

[0043] The spectra of certain of these higher-order derivative waveformshave negligible content at lower frequencies and therefore possess thehighly desirable property of avoiding radio frequency interference tolower-frequency services (e.g., television, radio-astronomy, cellulartelephones, and general communications) in the VHF and UHF regions ofthe radio frequency spectrum. This constitutes a major advantage of theinvention.

[0044] Since the derivative order and the shaping properties of theantenna, together with the width of the initial pulse, uniquelydetermine the spectral properties of the transmitted energy, a receiveremploying these parameters can be designed to optimally locate andextract the transmitted energy and convert it into a sharply definedreceived pulse. The concept of processing gain, normally used inspread-spectrum applications, applies here also in that the bandwidth ofthe transmitted pulse can be very large, extending over many potentialinterferers, each of which overlaps the transmitted energy onlymarginally. The bandwidth of the transmitted pulse is typically mademuch larger than most interferers, even those usually thought of asbroadband, such as standard direct-sequence spread-spectrum (DSSS)transmissions. Thus, even though there is very little energy per Hertzin the transmitted pulse, this energy per Hertz multiplied by thebandwidth of the pulse, which is also the receiver bandwidth, issufficient to identify the presence or absence of a transmitted pulse,allowing both its relative arrival time and particular shape to bedetermined. Standard readily commercially implementable methods oftime-domain correlation are sufficient for this purpose.

Bandwidth and Position as a Function of Pulse Width

[0045] The invention allows both the bandwidth and position in frequencyof an individual pulse to be determined. The ability to generatehigher-order derivatives is key to steering the bandwidth of thetransmitted energy as desired in frequency space. An additional benefitof using derivatives is that, by starting with a rectangular pulse oflonger duration, which is much easier and cheaper to handleelectronically, the location in frequency now becomes a function of thederivative order. By restricting the transmitter to the first-ordercase, as in existing art, bandwidth and center frequency are solelydetermined by pulse width.

[0046]FIG. 2 shows a high-level conceptual schematic of one possibilityfor generating a second-derivative Gaussian wavelet pulse, starting witha rectangular differential pulse of duration τ at the input. Thiscircuit shapes and transmits the pulse. In more detail, the rectangulardifferential pulse is generated by a signal source 210. The signalsource is coupled to a filter 220. The filter 220 is coupled to theoutput via a capacitor C. A resistor R is coupled to the output inparallel with the capacitor C. At the output is the desired pulse shape,which may then be amplified in a broadband radio frequency amplifier andpassed to the antenna.

[0047]FIG. 3 shows center frequency as a function of derivative order.If the characteristic time, τ, is 1 ns, the units of the ordinate are in10⁹ Hz (GHz). The center frequency of a pulse with characteristic time τand order n is {square root}{square root over (n)}/τ. This variationwith order is shown in FIG. 3 for τ=1.

[0048]FIG. 4 shows the behavior of the relative bandwidth as a functionof derivative order. At derivative orders higher than about 5, therelative bandwidth is less than approximately 50%. The relativebandwidth is only weakly dependent on τ. The 3-dB bandwidth for a givenpulse width, T, is a smooth but complicated function of τ and n; it isshown in FIG. 4. Note that the bandwidth for the n=1 pulse isconsiderably larger than for pulses with higher n. This feature isdesirable if only the first derivative Gaussian pulse is employed, butprovides no particular benefit when higher or multiple orders are used.

[0049]FIG. 5 shows the power spectrum of a 7th order Gaussian pulse withcharacteristic time of 2 ns. The frequency (X-axis aka abscissa) is inunits of 10⁹ Hertz (GHz). The pulse is centered at 1.3229 GHz and has abandwidth of 2.6677 GHz. For comparison, the first-order derivative usedin certain existing devices is shown as the dashed curve. Note that thepulse derived according to the existing art has much more energy atfrequencies below about 500 MHz and will tend to contribute significantinterference to services in that region (e.g., television, aircraft andpublic-service radios, and so forth).

Single Pulse—1 Bit Per Symbol

[0050] Prior-art techniques in the field of time-domain communicationsmake exclusive use of the first derivative of a Gaussian function. Therelative arrival times, referred to that of the preceding pulse(s)received, contain the data (message or information) transmitted. Theinvention neither makes use of the first derivative pulse nor encodesinformation via relative arrival times, preferring to allow arrivaltimes to be determined by the dispersive and reflective characteristicsof the physical channels and specifically avoiding the first derivativepulse due to its low-frequency nature.

[0051] The presence of derivative pulses of various orders constitutesfrequency-spectrum modulation and is completely independent of thesignaling-pulse timing which defines prior-art pulse time modulationmethods. Indeed, the prior-act systems all employ pulse-position orpulse-time modulation of one variety or another, including pulseedge-timing modulation. The time-averaged power spectra of theseprior-act signals are essentially stationary for random-data modulation,although the overall spectral width is strongly (inversely) dependent onthe basic generating-pulse width. The average power spectrum of theindividual first-order Gaussian derivative pulses is also highlydependent on the pulses-to-pulse time deviation (pulse time or positionmodulation). For small deviations, the spectrum is more concentratedaround the center frequency corresponding to the average pulserepetition rate, whereas at higher deviations (approaching the averagepulse-to-pulse interval), the spectrum is more spread out (dispersed).

[0052] The spectra of higher-order derivative pulses are, in general,much broader and more uniform (better dispersed) than the prior-artsignals. Except for the low-frequency limitations, which are oftenhighly desirable, the higher-order pulse spectra are more continuous andless “multi-line” in nature than competing technologies; they thereforemore closely resemble the spectrum of true random noise and thus providebetter signal concealment (low probability of detection).

Multiple Pulses-Multiple Bits Per Symbol

[0053] Significantly, due to the different pulse shapes /occupying thedifferent frequency bands, higher-order pulses are identifiable by shapeas belonging to a particular derivative order. FIG. 6 showsGaussian-derivative, time-domain pulses of order 4, 8, 12, 16, and 20.The underlying Gaussian function is shown as a dashed line. As nincreases, the width at zero time decreases, indicating increasingfrequency. The abscissa values are in units of the width of the initialsquare pulse.

[0054] The technique of transmitting several pulses, each with adifferent derivative order, at the same time, is equivalent totransmitting a vector pulse or a code-word symbol having more that onebit. This capability immediately opens up a much higher data rate thanis possible with a system based on a single Gaussian-derivative pulse.

[0055] The invention circumvents both the noise-susceptibility and theincreased-power problems of existing multi-state data quadratureamplitude (m-QAM) modulations by using mutually orthogonal states foreach bit transmitted. In addition, each pulse has two distinctquadrature phases, effectively doubling the bits-per-symbol figure ofmerit. This orthogonality is an inherent property of the Hermitepolynomials that underlie the pulse shape of the Gaussian-derivativefunctions.

[0056]FIG. 7 shows 7 time-domain pulses for the orders 2 through 8 (thedashed curves are of even order). The seven superimposed Gaussianderivative pulses of orders 2 through 8 compose a set of symbol codesfor transmitting 2⁷=128 different possible symbols in a single compositepulse, or 255 possible symbols when pulse phase is used.

[0057]FIG. 8 shows the combination, by simple addition, of the pulsesfor orders 3, 5, 6, and 8, thereby encoding the binary symbol 0101101 inthe sum for transmission. The abscissa is in units of the characteristictime. It can be appreciated that the combined pulse looks nothing likeany of the original pulses.

[0058]FIG. 9 shows the power spectral density of the composite pulserepresenting the binary code 0101101. The abscissa is in GHz for acharacteristic time of 1 ns. The power-spectral density extends (at the−20-dB level) or 1%-power point approximately over 3.85 GHz for acharacteristic time τ of 1 ns. The information in this frequency bandmay be extracted at the receiver by simply effecting a correlation inparallel of the received pulse with the pulses comprising the set ofsymbol codes. Since set is orthogonal when all members have the samecharacteristic time τ, the result of such a correlation will showmaximally strong peaks at just the code values transmitted. A specificimplementation of this approach is detailed in later pages.

[0059] Suppose that the above pulse is received and processed with anarray of correlators. The output of the array, in the absence ofinterferers and other noise, reproduces the binary code exactly at zerocorrelation lag. To obtain knowledge of the time of the zero lag, aprecursor pulse based on a single derivative Gaussian wavelet can betransmitted at a precisely known time several time constants prior tothe transmission of the composite pulse. The precursor pulse is thenused by the receiver to synchronize on each message pulse and is anintegral part of the coding scheme. For example, a receiver tuned to aslightly different precursor would attempt to decode the composite pulsewith an incorrect lag value, obtaining nonsense for the decoded symbol.Correct correlation also requires a suitable integrating function thatis implemented in electronic circuitry much as the derivative pulseswere derived: decoding then becomes a simple matter of correlating theincoming pulse in parallel with multiple candidate pulses.

[0060] Thus, a series of non-interfering (orthogonal) pulses can betransmitted simultaneously and subsequently received and decodedsimultaneously, allowing multiple bits per transmitted symbol to becommunicated. A parallel correlator will respond appropriately in thepresence of both broad- and narrow-band interferers.

Examples

[0061] Specific embodiments of the invention will now be furtherdescribed by the following, nonlimiting examples which will serve toillustrate in some detail various features of significance. The examplesare intended merely to facilitate an understanding of ways in which theinvention may be practiced and to further enable those of skill in theart to practice the invention. Accordingly, the examples should not beconstrued as limiting the scope of the invention.

Transmitter Architecture

[0062]FIG. 10 shows a block diagram of a transmitter in the preferredembodiment, where derivative-pulse generators of orders 2 through 8 areused to generate 7 separate parallel-path signals, each corresponding toa specific derivative-order signal. (The number seven is chosen by wayof example and is in no way limiting.) Looking at the overall signalflow, a digital data stream at lower left enters encoder 1007 to beprocessed and augmented by error detection/correction bits, framingbits, and such. The encoded output from 1007 feedsspreader/demultiplexer/router block 1008, which via a predeterminedalgorithm and/or logic configuration processes and sorts the encodeddata bits or units into 7 separate data streams 1013, which in turn feedeach of the 7 parallel data-modulator blocks 1004.

[0063] Meanwhile, a master clock oscillator 1001 generates stable timingsignals to control trigger generator 1002, which determines the pulsetransmission timing interval. In this embodiment of the invention, thesepulses have uniform time spacing and thus constitute a stable,single-frequency, unmodulated trigger or clock source to drive the 7parallel derivative pulse generators 1003 through the interveningprogrammable delay generator 1005. This block permits the relativephases of the 7 derivative pulses to be individually adjusted in astatic sense but in this implementation is not used for modulationpurposes. An additional output from 1005 feeds synchronization pulsegenerator 1006, which at a preselected time produces a specific-formatsync pulse to assist the associated receiver in data recovery at theother end of the transmission link.

[0064] The 7 aforementioned derivative-pulse generators 1003, designatedby the derivative orders (2 through 8), each take the 7 independenttrigger pulses and produce a shaped derivative (Gaussian or otherwise)pulse of the shapes shown in FIG. 6. These shaped pulses are sent to theaforementioned information modulator blocks 1004, designated by thenumber of the respective derivative-order pulse being processed. Thegroup of 7 encoded and routed modulation signals of group 1013 are alsofed to their respective modulators in block 1004. Each of the signals of1013 may be analog or digital, binary, ternary or multistate, asappropriate for the specific application.

[0065] Each modulator block in the group 1004 may implement analogmodulation (i.e., amplitude, frequency, or phase—amplitude modulation(AM) , frequency modulation (FM) or phase modulation (PM) or digitalmodulation forms such as binary phase-shift keying (BPSK), phase-shiftkeying, FSK, minimum-shift keying (MSK) for standard binary signals. Inaddition, more complex multistate modulation formats such as quadraturephase-shift keying (QPSK), offset quadrature phase-shift keying (OQPSK),quadrature amplitude modulation, multi-state data quadrature amplitudemodulation, multi-state data phase-shift keying (MPSK), multi-state datafrequency-shift keying (MFSK) and others are also quite useful in someapplications. In addition, amplitude-shift-keying (ASK), on-off keying(OOK) and others may be applied via straightforward techniques familiarto those skilled in the art. Further, ternary (3-state) and othermulti-level modulations can be extremely useful in achieving thederivative-pulse modulation. Since a key aspect to the invention is themutual orthogonality (statistical independence) of the variousderivative-pulse signals, the use of on-off keying, or in combinationwith standard binary phase-shift keying modulation (0° or 180° shift) isespecially beneficial in optimizing the inter-signal orthogonality,since the normal derivative signal (noninverted state), invertedderivative signal (inverted state), or no signal at all (“doff” state)are all orthogonal, even with data modulation. This combination ofmodulation states is particularly advantageous for use of ternary datastates (+1, 0, =1). This modulation may be standard data, PN sequencesor spread-data sequences as well.

[0066] The outputs of the parallel data modulators are combined with thepreviously mentioned sync pulse (from 1006) in summer/combiner block1009, which is typically a straightforward linear added device but whichmay in some cases be implemented via digital switching means (dependenton the relative timing of the pulse set or other system consideration).The output from summer 1009 is then amplified up to an appropriate powerlevel by amplifier 1010, which in turn feeds the transmitting antenna1012 through matching network 1011, according to typical practice.

[0067]FIG. 11 shows a corresponding receiver according to the presentinvention. The radio frequency signal is received by antenna 1101,coupled though matching network 1102 and processed by conventionalhigh-gain radio-frequency circuitry in receiver front-end block 1103.This device provides tuning adjustments, filtering automatic gain- andfrequency-control functions, and overall control to produce astable-amplitude, relatively low-noise wideband signal at 1104 which isrouted to the 7 parallel synchronous pulse-correlation detectors ingroup 1109. Meanwhile, the output of 1103, line 1104, feeds asynchronization subsystem block 1105 which recovers the predeterminedsync pulse, locks to the timing signal embedded therein, and correctsthe frequency of the master receiver-system clock 1106. The master clockin turn controls the timing of the trigger generators (one for eachderivative-pulse generator) at 1107. Each trigger pulse initiates thegeneration of the appropriate derivative-pulse generator block in group1108, which is designed to produce the same precise pulse shape as itscorresponding unit 1003 in the transmitter system of FIG. 10. Again inFIG. 11, the outputs of all 7 pulse generators at 1108 are fed into thereference inputs of the corresponding synchronous pulse correlators ingroup 1109. These detectors correlate, integrate, and filter therespective received pulses with their locally generated versions andimplement decision logic functions to produce the respective dataoutputs at 1113. These 7 output-decision signals, representing the 7detected information streams (assumed digital for the moment), arecombined/decoded/assembled in data multiplexer block 1110 to produce afinal series bitstream output at 1111. Meanwhile, the assembled datastream at 1111 is fed back through line 1112 to the synchronizer blockat 1105 to assist in system sync lock-up (acquisition) and tracking. Forspread-spectrum signals, the final output stream 1111 may be sent to acommon despreader 1113 to extract the original data from the compositespread-spectrum clipstream. Alternatively, each corrector/detectormodule in group 1109 can be equipped with a conventional amplitude-shiftkeying, frequency-shift keying, phase-shift keying, quadraturephase-shift keying, offset quadrature phase-shift keying, minimum-shiftkeying, multi-state data phase-shift keying, multi-state datafrequency-shift keying, multi-state data quadrature amplitudemodulation, or other appropriate type of data demodulator to extractmodulation information from the correlated derivative-pulse outputs; inthis case, the demodulated (unspread) data would appear on the parallelpaths designated 1113. In the case of spread-spectrum modulation on eachof the derivative signals, a spread-spectrum decoder would be insertedwithin each detector block in 1109 between the data-demodulation and theoutput points feeding lines 1113. An optional despreader 1113 is coupledto the stream 1111 and despread data out 1114.

[0068]FIG. 12 shows a first transmitter block diagram where thehigher-order derivative-pulse shaping features of the present inventionare applied to existing-art devices to improve their bandwidthefficiency or reduce interference to other users and bands. The outputof the fast-pulse block is presented to a specialized Nth-order Gaussian(or other) filter circuit (either passive or active) of an appropriateshape to produce the desired higher-order (i.e., 2nd or above)Gaussian-derivative or other selected pulse shape.

[0069]FIG. 12 shows a high-speed clock 1210 used to provide triggeringand synchronization that is coupled through a digital frequency dividerto both a pseudorandom polynomial generator block 1220 and aprogrammable delay circuit 1240 to permit adjustment of the actualfast-pulse timing. The delay circuit 1240 is coupled to a fast-pulsegenerator block 1250. The frequency of the high-speed clock 1210 is onthe order of the inverse of the generator-stage output pulse duration.Serial digital data to be transmitted is modulo-2 multiplied by anexclusive-OR gate 1230 with the pseudorandom polynomial data streamemerging from the PN-generator block 1220. Internally, this includes astandard, serial shift-register with programmable feedback interconnectsplaced at appropriate points to produce one of several desired digitalpolynomials; the detailed design of this type of generator is well knownin the spread-spectrum communications and coding art and will not bediscussed further. Given that the block 1220 produces a desirablepseudorandom code sequence (e.g., a Gold, maximal-length, or Kasamicode), the output bit-stream (often termed chipping sequence todistinguish it from the conventional data bits), is XORed with the truedata bits and used to control the programmable delay circuit 1240 in asimilarly pseudorandom manner. This in turn forces the timing of theemerging narrow pulses from the pulse generator block 1250 to be variedaccording to the statistics of the PN code (altered by the data,obviously). Note that the actual width of the narrow (fast) pulses thePW control line can also be modulated by another external signal, suchas that obtained from a second PN generator circuit; this could employthe same or different codes as the original PN unit, and may also bemodulated by the actual data stream as required. The pulse generatorblock 1250 is coupled to a Gaussian filter 1260 which is coupled to aradio-frequency amplifier 1270 which is in-turn coupled to a matchingnetwork 1280 and an antenna 1290.

[0070]FIG. 13 shows a second transmitter block diagram of the samevariety. The only significant difference from the previous example isthat a master clock 1310 drives a programmable-delay monostablemultivibrator circuit 1320 (commonly termed a one-shot), which generatesa pseudorandom variable pulse width at its output. This pseudorandomvariable pulse width in turn time-modulates the trigger signal for theseparate fast-pulse generator 1350, which also may have its output pulsewidth controlled as before. The symbol “O/S” in FIG. 13 indicates theprogrammable delay “one-shot.” The master clock 1310 is also coupled toa divider 1330 which in-turn is coupled to the generator 1320 and theexclusive-OR gate 1330. As in the previous example, the pulse generatorblock 1350 is coupled to the Gaussian filter 1360 which is coupled tothe radio frequency amp 1370 which is in-turn coupled to the matchingnet 1380 and the antenna 1390. The principal reason for this alternateversion is to facilitate partitioning of the standard-speed and veryhigh-speed portions of the transmitter circuitry for optimum layout andfabrication as a custom integrated-circuit chip (ASIC).

Receiver Architecture

[0071]FIG. 14 shows a wideband or ultra-wideband (UWB) receiver forimplementing an embodiment of the invention corresponding to theprevious transmitters of FIGS. 12 and 13. A broadband radio frequencysignal from a receiving antenna 1400 is bandpass-filtered by a widebandfilter/low-noise amp 1410 to admit the desired frequency range andsimultaneously reject out-of-band signals and interference. AppropriateGaussian pulse-shaping and/or equalization may also be performed by thewideband filter/low-noise amp 1410. The following low-noise, front-endamplifier (LNA) then boosts the signal amplitude to a useful level. Anintegral automatic gain-control (AGC) loop 1420 that includes a peakdetector 1430 regulates the LNA's output to accommodate both high andlow input-signal levels while maintaining good amplifier linearity. TheLNA output also drives a synchronization-trigger detector circuit 1440which is used to start the synchronization process in the downstreamportion of the receiver system. Typically, a sync burst or preamble (orperhaps a specially configured data sequence) will be transmitted at ornear the beginning of each data block to facilitate rapidsynchronization and acquisition of the data stream in the receiver,although this is not absolutely mandatory. If a valid trigger signal isdetected, the pulse is gated by a gate 1450 through to a correlator1460. The correlator 1460 circuit performs the template-matching of theincoming Gaussian pulse stream with the selected-order pulse shape. Theoutput from the correlator 1460 then drives the following datademodulator/decoder 1465 to secure the desired output data stream.Additional signal tracking and synchronization are handled by acombination of a feedforward phase-lock synchronizer driven by thecorrelator output and a feedback locking path derived from the finalreceived data bitstream. The combined outputs drive a variable-frequencyclock 1480, which in turn, regulates the readout rate of a PN generator1490, thus acquiring (and maintaining) lock with the local PN sequencein time and phase to the incoming PN chipstream arriving from thetransmitter. Thus, FIG. 14 shows a receiver block diagram withsynchronization and demodulation details.

[0072] Note that adaption of standard readily commercially availabledirect-sequence spread spectrum receiver technology is suitable for someembodiments of the invention. Specifically, receiver methods presentlyknown to be used in spread-spectrum receivers are sufficient. Analternative approach is to employ an analog correlator based on thespectral properties of the precursor synchronization pulse. To avoidissues of time synchronization, this correlator 1460 can take the formof a matched filter having maximal response, relative to its inputpower, when a pulse of the desired shape is present.

[0073] While not being limited to any particular performance indicatoror diagnostic identifier, preferred embodiments of the invention can beidentified one at a time by testing for the ability to equalize thederivative shapes to various antenna and transmission-channelcharacteristics. Another way to seek preferred embodiments is to testthe ability of the broad spectrum being transmitted to be notchfiltered. Another way to seek preferred embodiments is to test forminimal dispersive effects.

Practical Applications of the Invention

[0074] A practical application of the invention that has value withinthe technological arts is clandestine communications due to its very lowtransmitted radio frequency power. Further, the invention is useful inconjunction with reliable communications in the presence of severemultipath interference, or in conjunction with high data rate spreadspectrum communications, or the like. There are virtually innumerableuses for the invention, all of which need not be detailed here.

Advantages of the Invention

[0075] A pulse transmission transceiver architecture for low powercommunications, representing an embodiment of the invention, can be costeffective and advantageous for at least the following reasons. Theinvention makes more practical (i.e., commercially feasible) the classof time-domain, spread spectrum communications. The inventionsignificantly reduces lower-frequency emissions from time-domain spreadspectrum communication modes, thereby reducing potentially harmfulinterference to existing radio frequency services and users. Theinvention can make greater receiver selectivity possible. The inventionalso makes transmission of multiple bits per time-domain symbolpossible.

[0076] All the disclosed embodiments of the invention described hereincan be realized and practiced without undue experimentation. Althoughthe best mode of carrying out the invention contemplated by theinventors is disclosed above, practice of the invention is not limitedthereto. Accordingly, it will be appreciated by those skilled in the artthat the invention may be practiced otherwise than as specificallydescribed herein.

[0077] For example, although the time-domain transceiver architecturedescribed herein can be a separate module, it will be manifest that thetime-domain transceiver architecture may be integrated into thehardware/software with which it is associated. Further, all thedisclosed elements and features of each disclosed embodiment can becombined with, or substituted for, the disclosed elements and featuresof every other disclosed embodiment except where such elements orfeatures are mutually exclusive.

[0078] It will be manifest that various additions, modifications andrearrangements of the features of the invention may be made withoutdeviating from the spirit and scope of the underlying inventive concept.It is intended that the scope of the invention as defined by theappended claims and their equivalents cover all such additions,modifications, and rearrangements. The appended claims are not to beinterpreted as including means-plus-function limitations, unless such alimitation is explicitly recited in a given claim using the phrase“means-for.” Expedient embodiments of the invention are differentiatedby the appended subclaims.

What is claimed is:
 1. A method of pulse transmission communications,comprising: generating a pulse-signal waveform; transforming saidpulse-signal waveform into at least one higher-order derivativewaveform; and transmitting said at least one higher-order derivativewaveform as an emitted pulse.
 2. The method of claim 1, wherein said atleast one higher-order derivative waveform is modulated by an on/offinformation signal.
 3. The method of claim 2, further comprisingmodulating said at least one higher-order derivative waveform with ananalog technique selected from the group consisting of amplitudemodulation, frequency modulation, and phase modulation.
 4. The method ofclaim 2, further comprising modulating said at least one higher-orderderivative waveform with a digital binary technique selected from thegroup consisting of phase-shift keying, binary phase-shift keying,quadrature phase-shift keying, offset quadrature phase-shift keying,frequency-shift keying, minimum-shift keying, amplitude shift keying,and on-off keying.
 5. The method of claim 2, further comprisingmodulating said at least one higher-order derivative waveform with amulti-state technique selected from the group consisting of multi-statedata frequency-shift keying, multi-state data phase-shift keying,multi-state data quadrature amplitude modulation, ternary digitalmodulation, and n-state digital modulation.
 6. The method of claim 1,wherein transforming said pulse-signal waveform into said at least onehigher-order derivative waveform includes shaping a frequency spectrumof said emitted pulse to reduce lower frequency emissions.
 7. The methodof claim 1, wherein transforming said pulse-signal waveform into said atleast one higher-order derivative waveform includes orthogonallyencoding a single bit signal into said emitted pulse.
 8. The method ofclaim 1, wherein said at least one higher-order derivative waveform ismodulated by a multiple-bit signal.
 9. The method of claim 7, whereinorthogonally encoding a multiple-bit signal into said emitted pulseincludes adding a plurality of higher-order derivative waveforms thatare a function of said pulse-signal waveform.
 10. The method of claim 1,wherein said pulse-signal waveform represents a Gaussian function. 11.The method of claim 1, wherein said pulse-signal waveform is atime-domain function exp(−x^(2n)/2a), where x is the function in eachdomain, a is a constant, and n is an integer that represents an order.12. The method of claim 1, wherein transforming said pulse-signal intosaid at least one higher-order derivative includes transforming saidpulse signal with active circuitry.
 13. The method of claim 1, whereingenerating said pulse-signal waveform includes generating said pulsesignal waveform from a stored digital version.
 14. The method of claim1, further comprising repeating the step of generating said pulse-signalwaveform to achieve orthogonal time hopping.
 15. The method of claim 1,further comprising repeating at least one step selected from the groupconsisting of generating said pulse-signal waveform and transformingsaid pulse-signal waveform into said at least one higher-orderderivative waveform, to achieve orthogonal frequency hopping.
 16. Themethod of claim 1, further comprising repeating at least one stepselected from the group consisting of generating said pulse-signalwaveform and transforming said pulse-signal waveform into said at leastone higher-order derivative waveform, to achieve combined orthogonalfrequency-time hopping.
 17. An electromagnetic waveform, comprising: anemitted pulse that is produced from at least one higher-order derivativewaveform of a pulse-signal waveform.
 18. The electromagnetic waveform ofclaim 17, wherein a frequency spectrum of said emitted pulse is shapedto reduce at least one member selected from the group consisting oflower frequency emissions and higher frequency emissions.
 19. Theelectromagnetic waveform of claim 17, wherein said emitted pulseorthogonally encodes a multiple-bit signal.
 20. The electromagneticwaveform of claim 19, wherein said multiple-bit signal is encoded intosaid emitted pulse by adding a plurality of higher-order derivativewaveforms that are a function of said pulse-signal waveform.
 21. Theelectromagnetic waveform of claim 17, wherein said pulse-signal waveformis a Gaussian function.
 22. The electromagnetic waveform of claim 17,wherein said pulse-signal waveform represents a time-domain functionexp(−x^(2n)/a), where x is the function in each domain, a is a constant,and n is an integer that represents an order.
 23. An orthogonaltime-hopping electromagnetic waveform that includes the electromagneticwaveform of claim
 17. 24. An orthogonal frequency-hoppingelectromagnetic waveform that includes the electromagnetic waveform ofclaim
 17. 25. A combined orthogonal frequency-time hoppingelectromagnetic waveform that includes the electromagnetic waveform ofclaim
 17. 26. A pulse transmission transmitter, comprising: a clock; atrigger signal generator coupled to said clock; at least onehigher-order derivative pulse generator coupled to said trigger signalgenerator; a selector circuit coupled to said at least one higher-orderderivative pulse generator; and an output-interface device coupled tosaid at least one higher-order derivative pulse generator.
 27. The pulsetransmitter of claim 26, further comprising a programmable delay circuitcoupled to said trigger signal generator.
 28. The pulse transmitter ofclaim 26, further comprising at least one information modulator circuitcoupled to said at least one higher-order pulse generator wherein saidat least one information modulator circuit provides at least onefunction selected from the group consisting of amplitude modulation,frequency modulation, phase modulation, digital binary modulation,phase-shift keying, binary phase-shift keying, quadrature phase-shiftkeying, offset quadrature phase-shift keying, frequency-shift keying,minimum-shift keying, amplitude shift keying, on-off keying, multi-statedata frequency-shift keying, multi-state data phase-shift keying,multi-state data quadrature amplitude modulation, ternary digitalmodulation, and n-state digital modulation.
 29. The pulse transmitter ofclaim 26, further comprising at least one summation circuit coupled tosaid at least one higher-order derivative pulse generator.
 30. The pulsetransmitter of claim 29, wherein said at least one summation circuitincludes at least one member selected from the group consisting of apassive combiner, an active summing circuit, and a digital combiningcircuit.
 31. The pulse transmitter of claim 26, further comprising apower amplifier coupled to said at least one higher-order derivativepulse generator.
 32. The pulse transmitter of claim 26, furthercomprising data encoder circuitry coupled said at least one higher-orderderivative pulse generator.
 33. The pulse transmitter of claim 28,further comprising data encoder circuitry coupled to said at least oneinformation modulator circuit.
 34. The pulse transmitter of claim 28,further comprising a spread-spectrum data modulator coupled to said atleast one information modulator circuit.
 35. The pulse transmitter ofclaim 34, wherein said spread-spectrum data modulator provides at leastone spread-spectrum mode selected from the group consisting of directsequence, frequency hopping, and time-hopping.
 36. The pulse transmitterof claim 26, including a demultiplexer coupled to said at least onehigher-order derivative pulse generator.
 37. The pulse transmitter ofclaim 28, further comprising a demultiplexer coupled to said at leastone information modulator circuit.
 38. The pulse transmitter of claim29, further comprising a synchronization-pulse generator coupled to saidat least one summation circuit.
 39. The pulse transmitter of claim 26,further comprising a matching network connected to said output-interfacedevice.
 40. The pulse transmitter of claim 26, wherein saidoutput-interface includes an antenna.
 41. The pulse transmissiontransmitter of claim 27, wherein said programmable delay circuitincludes a programmable-delay monostable multivibrator circuit.
 42. Thepulse transmission transmitter of claim 26, wherein said at least onehigher-order derivative pulse generator includes a filter.
 43. The pulsetransmission transmitter of claim 42 where said filter includes aGaussian filter.
 44. A one-chip integrated circuit including the pulsetransmission transmitter of claim
 26. 45. A pulse transmission receiver,comprising: a front-end amplification/processing circuit; asynchronization circuit coupled to said front-endamplification/processing circuit; a clock coupled to saidsynchronization circuit; a trigger signal generator coupled to saidclock; and at least one higher-order derivative pulse generator coupledto said trigger signal generator.
 46. The pulse transmission receiver ofclaim 45, further comprising at least one received pulse detectioncircuit coupled to said at least one higher-order derivative pulsegenerator.
 47. The pulse transmission receiver of claim 46, wherein saidat least one received pulse detection circuit includes a synchronouspulse correlator.
 48. The pulse transmission receiver of claim 47,wherein said at least one higher-order derivative pulse generatorincludes a data demodulator.
 49. The pulse transmission receiver ofclaim 48, wherein said data demodulator provides at least one functionselected from the group consisting of amplitude demodulation, frequencydemodulation, phase demodulation, digital binary demodulation,phase-shift keying, binary phase-shift keying, quadrature phase-shiftkeying, offset quadrature phase-shift keying, frequency-shift keying,minimum-shift keying, amplitude shift keying, on-off keying, multi-statedata frequency-shift keying, multi-state data phase-shift keying,multistate data quadrature amplitude demodulation, ternary digitaldemodulation, and n-state digital demodulation.
 50. The pulsetransmission receiver of claim 45, further comprising a programmabledelay circuit connected between said trigger signal generator and saidat least one higher-order derivative pulse generator.
 51. The pulsetransmission receiver of claim 45, including a multiplexer coupled tosaid at least one higher-order derivative pulse generator.
 52. The pulsetransmission receiver of claim 51, further comprising a data despreadercoupled to said multiplexer.
 53. The pulse transmission receiver ofclaim 52, further comprising a connection between said data despreaderand said synchronization circuit adapted to provide automaticfrequency/synchronization control.
 54. The pulse transmission receiverof claim 45, further comprising a matching network connected to saidfront-end amplification/processing circuit;.
 55. The pulse transmissionreceiver of claim 54, further comprising an antenna coupled to saidmatching network.
 56. The pulse transmission receiver of claim 45,wherein said at least one higher-order derivative pulse generatorincludes a filter.
 57. The pulse transmission receiver of claim 56 wheresaid filter includes a Gaussian filter.
 58. A one-chip integratedcircuit including the pulse transmission receiver of claim
 45. 59. Amethod of pulse transmission communications, comprising: generating apulse position modulated signal waveform; transforming said pulseposition modulated signal waveform into at least one higher-orderderivative waveform; and transmitting said at least one higher-orderderivative waveform as an emitted pulse.
 60. The method of claim 59,wherein transforming said pulse position modulated signal waveform intosaid at least one higher-order derivative waveform includes shaping afrequency spectrum of said emitted pulse to reduce lower frequencyemissions.
 61. The method of claim 59, wherein transforming said pulseposition modulated signal waveform into said at least one higher-orderderivative waveform includes orthogonally encoding or modulating asingle bit signal into said emitted pulse.
 62. The method of claim 61,wherein orthogonally encoding a multiple-bit signal into said emittedpulse includes adding a plurality of higher-order derivative waveformsthat are a function of said pulse-signal waveform.
 63. The method ofclaim 59, wherein said pulse position modulated signal waveformrepresents a Gaussian function.
 64. The method of claim 59, wherein saidpulse-signal waveform is a time-domain function exp(−x^(2n)/a), where xis the function in each domain, a is a constant, and n is an integerthat represents an order.
 65. The method of claim 59, whereintransforming said pulse position modulated signal into at least onehigher-order derivative includes transforming said pulse positionmodulated signal with active circuitry.
 66. The method of claim 59,wherein generating said pulse position modulated signal waveformincludes generating said pulse position modulated signal from a storeddigital version.
 67. The method of claim 59, further comprisingrepeating the step of generating said pulse position modulated signalwaveform to achieve orthogonal time hopping.
 68. The method of claim 59,further comprising repeating at least one step selected from the groupconsisting of generating said pulse position modulated signal waveformand transforming said pulse position modulated signal waveform into saidat least one higher-order derivative waveform to achieve orthogonalfrequency hopping.
 69. An electromagnetic waveform, comprising: anemitted pulse that is produced from at least one higher-order derivativewaveform of a pulse position modulated signal waveform.
 70. Theelectromagnetic waveform of claim 69, wherein a frequency spectrum ofsaid emitted pulse is shaped to reduce lower frequency emissions. 71.The electromagnetic waveform of claim 69, wherein said emitted pulseorthogonally encodes a multiple bit signal.
 72. The electromagneticwaveform of claim 71, wherein said multiple bit signal is encoded intosaid emitted pulse by adding a plurality of higher-order derivativewaveforms that are a function of said modulated pulse-signal waveform.73. The electromagnetic waveform of claim 69, wherein said pulseposition modulated signal waveform represents a Gaussian or otherappropriate mathematical function.
 74. An orthogonal time-hoppingelectromagnetic waveform that includes the electromagnetic waveform ofclaim
 69. 75. An orthogonal frequency-hopping electromagnetic waveformthat includes the electromagnetic waveform of claim
 69. 76. A pulsetransmission transmitter, comprising: a clock; a pseudorandom polynomialgenerator coupled to said clock, said pseudorandom polynomial generatorhaving a polynomial load input; an exclusive-OR gate coupled to saidpseudorandom polynomial generator, said exclusive-OR gate having aserial data input; a programmable delay circuit coupled to both saidclock and said exclusive-OR gate; a pulse generator coupled to saidprogrammable delay circuit; a filter coupled to said pulse generator;and an antenna coupled to said matching network.
 77. The pulsetransmission transmitter of claim 76, wherein said programmable delaycircuit includes a programmable-delay monostable multivibrator circuit.78. The pulse transmission transmitted or claim 76, herein said filterincludes a Gaussian filter.
 79. The pulse transmitter of claim 76,wherein said clock, said pseudorandom polynomial generator, saidexclusive-OR gate, said programmable delay circuit, said pulse generatorand said filter all compose a one-chip integrated circuit.
 80. A pulsetransmission receiver, comprising: a correlator; a demodulation decodercoupled to said correlator; a clock coupled to said demodulationdecoder; and a pseudorandom polynomial generator coupled to both saidcorrelator and said clock.
 81. The pulse transmission receiver of claim80, further comprising a gate coupled to said correlator.
 82. The pulsetransmission receiver of claim 81, further comprising a trigger coupledto said correlator.
 83. The pulse transmission receiver of claim 82,further comprising an integral automatic gain-control loop coupled toboth said gate and said trigger.